1. Field of the Invention
The present invention relates to carbon nanotubes and a method of manufacturing the same, an electron emission source, and a display.
2. Description of Background Art
Conventionally, a field electron emission source in which emitters are disposed between a cathode electrode and a gate electrode and electrons are emitted from the emitters by applying a voltage between the cathode electrode and the gate electrode has been developed.
The field electron emission source has excellent features such as low power consumption and long lifetime in comparison with an electron source which utilizes thermal energy (thermionic emission source). As a material widely used for the electron emission source, semiconductors such as silicon (Si), metals such as tungsten (W) and molybdenum (Mo), a polycrystalline diamond thin film, and the like are known.
When an electric field of about 109 V/m is applied to the surface of a metal or a semiconductor, electrons pass through a barrier using a tunneling effect, whereby the electrons are emitted under vacuum even at ordinary temperature (field emission phenomenon). Therefore, the extracting current is determined depending upon the electric field applied to an emission section (emitter) from an extracting electrode section (gate electrode). It is known in the art that a field intensity applied to the emitter is increased as the tip of the emitter becomes sharper. Therefore, it is necessary to process the tip of the electron emission section formed of a semiconductor or a metal into the shape of a sharp needle.
In order to enable stable field emission, the operational atmosphere must be maintained at high vacuum of 133×10−8 Pa or more.
Carbon nanotubes have attracted attention as a material for the electron emission source from the above point of view. The outer diameter and the length of the carbon nanotubes are 10 to several tens of nanometers and several microns, respectively. Therefore, the carbon nanotubes have a structure which enables field emission at a low voltage. Moreover, carbon is chemically stable and has mechanical strength. Because of this, the carbon nanotube is an ideal emitter material.
However, since the carbon nanotubes are manufactured by using an arc discharge method or laser irradiation to graphite and used after purification, there have been the following problems.
A conventional manufacturing method for the carbon nanotubes incurs considerable cost. Moreover, yield of the carbon nanotubes is extremely low due to a high content of impurities. Therefore, cost of the resulting carbon nanotubes is inevitably increased. This makes an electron emission source manufactured by using the carbon nanotubes unprofitable.
There may be a case where a paste of carbon nanotubes is printed on a specific electrode as the electron emission source. However, the carbon nanotubes are aligned parallel to the substrate after printing due to viscosity of a solvent of the printing paste or additives. This results in problems such as an insufficient field emission effect, an increase in extracting voltage, and a decrease in extracting current.
As a method of directly depositing the carbon nanotubes on the substrate, a microwave plasma method and a direct current plasma method have been proposed. However, it is difficult to uniformly deposit the carbon nanotubes over a wide area of the substrate by using these methods. Moreover, the temperature of the substrate is inevitably increased in order to deposit the carbon nanotubes in a plasma stream at about 133 Pa. This makes it difficult to use a substrate having a softening point of about 500° C.
The present invention has been achieved to solve the above conventional problems.
Accordingly, an object of the present invention is to provide carbon nanotubes which are perpendicularly deposited on a substrate and manufactured without excessively increasing the temperature of the substrate.
Another object of the present invention is to provide a method of manufacturing carbon nanotubes which are uniformly deposited over a wide area, have a regular crystal structure, and are aligned perpendicularly to a substrate, even if the temperature of the substrate is 500° C. or less.
Still another object of the present invention is to provide an electron emission source excelling in electron emission characteristics obtained by using the carbon nanotubes.
Yet another object of the present invention is to provide a display using the electron emission source.